Stool or fecal samples are routinely tested for the presence of parasites, fat, occult blood, viruses, bacteria and other organisms and chemicals in the diagnosis for various diseases. The stool is usually collected, placed in a clean container and processed for testing.
Stool collection is usually non-invasive and theoretically ideal for testing pediatric or geriatric patients, for testing away from a clinical site, for frequently repeated tests and for determining the presence of analytes which are likely to be found in the digestive tract. Stool can also be collected with a swab or finger cot during examination and applied directly to a test surface. For microscopic examination or occult blood testing, the sample can be spread directly on a test surface. For other tests, such as testing for fat, the stool may be suspended in a liquid medium such as water.
Traditional sample examinations have used complex chemical or microbiological procedures. These procedures are being rapidly replaced with immunoassay methods. Immunoassay techniques are highly sensitive and require only a small sample. Solid-phase techniques such as latex agglutination and enzyme immunoassays have been developed to such a stage of simplicity that they can be performed at home, at the doctor's office or other test sites without the need for highly trained laboratory technicians or expensive instruments. Application of solid-phase immunoassay procedures to the analysis of stool samples is thus highly desirable.
Application of immunoassay techniques to fecal analysis has proven to be difficult for several reasons. Stool handling is disagreeable and biohazardous, and sanitary and inoffensive procedures for processing stool have proven to be awkward and frequently complex. Analytes in stool samples are frequently unstable. Weighing, extracting and centrifuging, and storing samples are difficult except in a clinical laboratory equipped with suitable apparatus and skilled technicians.
Constituents of stool are known to interfere with solid-phase immunoassays. Immunoreactants immobilized on solid-phase are desorbed by stool constituents. Non-specific reactions occur.
To increase the commercial use of immunoassay techniques for measuring analytes in stool, a number of problems must be solved. Instability of the analyte in the stool, interference from stool constituents, needs for extensive handling of the stool, equipment contamination, and instrumentation needs must be minimized. Simple preparation steps avoiding the use of expensive equipment and instruments are required to extend the use of immunoassay testing procedures to sites outside hospital and clinical laboratory environments.